Small-field Dosimetry of 6- and 10-MV Flattening Filter-free and Flattening Filter Photon Beams for Therapeutic Use

Abstract

This investigation aimed to measure and commission small unflat photon beams using the detectors described in our previous study10. Furthermore, the dosimetric parameters of small-field unflat and flat photon beams were compared to provide a better interpretation of beam energy and spectrum. The TrueBeam linear accelerator (TrueBeam LINAC, Varian Medical Systems) was employed in this study. The 10 and 6 MV unflat and flat photon beams were used to measure the output factor, depth dose, and beam profile of small-fields ranging in size from 1 cm × 1 cm to 6 cm × 6 cm. All measurements were performed according to the TRS-483 protocols established by the International Atomic Energy Agency. For both 10 and 6 MV, the output factors in unflat beam were significantly higher than in flat beam. The study found that unflat beam penumbras were slightly smaller than flat beam penumbras for both photon energies, which may improve tumor conformity and reduce doses to normal organs. The unflat photon beams had higher suface doses and lower depth doses at 10 cm than the flat photon beams for both energies, leading to considerably more beam energy degradation for unflat beams. The findings of this work are consistent with previously published data, and they will be useful for future research and LINAC commissioning.